Hillary Rodham Clinton said Wednesday that she understood why people had questions about her decision to use only private email while she was secretary of state and that she took responsibility for that decision, a shift from her past remarks about an issue that has dogged her since shortly before she began her presidential campaign.

Her remarks, made during a campaign stop in Iowa, came as Mrs. Clinton has faced growing criticism for making light of her email use, which Democrats fear has become an albatross on her hopes of winning the White House. “What, like with a cloth or something?” she said to a Fox News reporter last week who had asked whether she had “wiped,” or erased, her email server before turning it over to the F.B.I. recently.

“I know people have raised questions about my email use as secretary of state, and I understand why,” Mrs. Clinton said Wednesday. “I get it. So here’s what I want the American people to know: My use of personal email was allowed by the State Department. It clearly wasn’t the best choice. I should’ve used two emails: one personal, one for work.”